The five Purple Medals in Eiji's body are invisible to X-rays. It's assume that current human technology is unable to detect Core Medals. Maybe that's why the Gorilla Candroid is unable to detect Greeeds.

Eiji is a son of a politician and raised money for needy countries. One of the fundraisers was used to fund a civil war that he was caught in and risked his life to protect a village. Behind the scenes, Eiji's parents paid a ransom so Eiji would be returned safely. Date was at the hospital where he saw Eiji leaving with a bunch of men in suits.

Due to the incident, it made Eiji dry up inside and having really no desires. This is why Kougami thinks Eiji is perfect for OOO since due to having no desires, he won't go out of control. But with the Purple Medals being inside of him, Eiji could out of control.

The Purple Medals are made of up extinct animals (dinosaurs specifically). Their desire is nothingness.

Eiji uses the Putotyra Combo for the first time. The Purple Medals have a will of their own and able to insert themselves into the OOO Driver by themselves. They can even move the Scanner by themselves.

Maki is the one who created the Pteranodon Yummies by inserting the other five Purple Medals into himself.

These Yummies were created by Maki most likely to test his power with the newly inserted Purple Medals inside of him. They are capable of flight and spewing fireballs. Also they can create a black smoke that can make humans disappear if caught in it.